Filament structure



H. D DOOLITTLE FILAMENT STRUCTURE 2 Sheets-Sheetl Filed April 2, 1949 www@ @EY SMMWS ATTORN EY Oct. 3l, 1950 H. D. DOOLITTLE Filed April 2, 1949 FILAMNT STRUCTURE 2 Sheets-Sheet 2 /pm Tb www ATTGRNEYS Patented Oct. 31, 1950 FILAMENT STRUCTURE Howard D. Doolittle, Stamford, IConn., assgnor to Machlett Laboratories Incorporated, Springdale, Conn., a corporation of Connecticut Application April 2, 1949, Serial No. 85,188

6 Claims. (Cl. Z50-27.5)

This invention relates to filament structures for use in electron tubes and is concerned more particularly with a novel filament structure of the self-supporting type, which may be advantageously employed in tubes for power purposes. In the new filament structure, difficulties arising from cross-radiation between closely adjacent portions of the filaments are overcome, so that the life of the structure is substantially increased.

Self-supporting filament structures for use in electron tubes include a plurality of filaments of tungsten wire, which are held at one end and extend parallel from their supports in a close series. The end portions of the filaments remote from the supports converge and are connected together at the axis of the series. The convergent portions of the filaments lie closer together and thus run hotter because of crossradiation, than the remainder of the filaments with the result that there is excessive evaporation from the convergent lengths of the laments and the life of the structure is thereby decreased.

The present invention is directed to the provision of a self-supporting structure, in which the radiating capacity of the convergent portions of the laments is increased, so that the operating temperatures of such parts is kept within acceptable limits. The increase in radiating capacity of the convergent lengths of the lilaments is 'obtained by increasing the radiating surface thereof and, for this purpose, the convergent parts of the filaments may be provided with individual windings of smaller wire or such wire may be interlaced with the filaments adjacent their junction point. With either arrangement, the parts of the filaments lying relatively close together are kept from becoming overheated.

For a better understanding of the invention, reference may be made to the accompanying drawings, in which:

Fig. 1 is a View partly in elevation and partly in section of a typical electron tube containing one form of the new filament structure;

Fig. 2 is an end View of the filament structure f Fig. l;

Fig. 3 is a sectional view on-the line 3 3 of Fig. 2;

Figs. 4, 5 and 6 are sectional views on the lines 4-4, 5 5, and 6--6, respectively, of Fig. l; and

Figs. 7 and 8 are an end view and a fragmentary elevational View of a modified form of the new filament structure.

The tube shown in Fig. 1 comprises an envelope, made up of a metallic anode section I0 having one end embedded in the end of a glassrsection II, through the wall of which are sealed four posts spaced apart Post I2 carries a circular plate I4 having a radial extension I4a attached to the end of the post and post I3 carries a plate I 5, which is formed with a scalloped edge and has a radial extension I5a attached to the end of the post. A plurality of rods I6, shown as 6 in number, are mounted on plate I4 at equal spacings along its periphery and plate I5 carries another group of rods Il, which lie in alternate relation to rods I6. The rods extend parallel at right angles to the plates and lengthwise of the tube. At its end, each rod carries a clip I8, which extends outwardly from the rod and supports one end of a filament I9. The twelve lilaments extend parallel in a closed series and, with the arrangement described, the filaments in the series are connected alternately to plates I4 and I5 and to posts I2, I3. At their ends remote from the supporting clips I8, the filaments are bent inwardly to converge and then reversely bent so that their extreme end portions lie paral lel and are secured to the surface of a metal-plug 20 by welding and by a wrapping of fine wire 2|.

The filaments lie within a grid structure comprising a circular series of wires 22 extending into the tubular portion 23 of a shield and secured to the inner surface of that portion. The shield has a radial flange 24 secured by bolts 25 to a pair of arcuate plates 26 carried on the ends of posts 21, 28, respectively, the posts being sealed throughthe wall of the glass section of the envelope. The ends of the wires 22 extend into a metal cup 29 and are secured to the inner surface thereof, and a wire 30 is wound helically around wires 22.

In a self-supporting iilament structure of the kind described, it is found that the convergent portions I9a of the filaments leading to plug 20 become overheated in operation because of crossradiation and, in the structure of the invention, this difficulty is overcome by increasing the radiating capacity of the convergent lengths of the filaments. In the construction shown in Figs. 1 to 3, inclusive, the heat radiating capacity of the converging portions of the filaments is increased by wrapping each such portion of the filament with a fine wire 3|. The additional radiating surface provided by the fine wire windings is suicient to prevent localized overheating Y of the filaments and the life of thel filament' structure is, accordingly, increased.

In the modified construction shown in Figs. '7 and 8, the heat radiating capacity of the convergent lengths ISia of the laments is increased by spirally interlacing a fine wire 32 with the convergent portions of the filaments. The wire 32 serves the same purpose as wires 3| in that it serves to radiate heat and thus keep the convergent portions of the laments from overheating. Wire 32 is interlaced with the laments in as many turns as are necessary to obtain the desired eiect.

The new lament structure is superior to prior self-supporting filament structures in that localized overheating of the laments is avoided, as explained above. The new structure is also superior to nlament structures of the type in which the inner ends of the laments are'vcon-V y nected to a plate acted on by a spring-pressed rod to maintain the laments taut during operation. In a structure of the latter type, the plate radiates so much heat that lengths 'ci Vthe filaments of from one-half inch to one inch adjacent the plate operate at a low temperature and efcient emission is not obtained from these parts of the laments. With the new structure, the iilaments may be kept at a uniform temperature throughout their length without overheating, so that a tube in which the new structure is used may operate at a higher power than tubes provided with the former structures, or else it may operate at the same power level but at a lower lament temperature and thus with increased life.

I claim:

1. In an electron tube, a iilament structure comprising a plurality of supports arranged in a closed series, a lament extending forward from each support, the filaments lying parallel having end portions remote from the supports which converge and terminate in parallel end sections, i,

means for securing said end sections together, and metallic flamentary elements engaging the converging portions only of the filaments, said elements addingV t0 the heat radiating capacity of said portions of the filaments.

2. In an electron tube, a lament structure comprising a plurality of supports arranged in a closed series, a -filament extending forward from each support, the filaments lying parallel and having end portions remote from the supports which converge and are connected together,

and a filamentary element wound around eachy filament only between its point of connection to the other filaments and its parallel portion, said lamentary element acting to increase the heat radiating capacity of that portion of the filament on which it is wound.

3. In an electron tube, a lament structure comprising a plurality of supports arranged in a closed series, a filament extending forward from each support, the iilaments lying parallel and having end portions remote from the supports which converge and are connected together, and a lamentary element wound around the convergent portion only of each lament and acting to increase the radiating capacity of said lament.

4. In an electron tube, a lament structure` comprising a plurality of supports arranged in a closed series, a lament extending forward from each support, the filaments lying parallel and having end portions remote from the supports which converge and are connected together, and a iilamentary element interlaced with the laments adjacent their point of connection to one another and increasing the heat radiating capacity of the laments.

5. In an electron tube, a filament structure comprising a plurality of supports arranged in a closed series, a lament extending forward from each support, the iilaments lying parallel and having end portions remote from the supports which converge and are connected together, and a lamentary element interlaced with the convergent portions only of said laments and acting to increase the heat radiating capacity of the filaments.

6. In an .electronic tube, a filament structure comprising a pair of plates mounted in spaced relation face to face, a plurality of supports mounted on each plate, the supports all extending in the same direction and. arranged in a closed series with alternate supports in the series mounted on one plate and intermediate supports mounted on the other, a lament attached to each support, thelaments extending parallel in a closed series at substantially right angles to the plates, the laments having portions remote from the supports, which converge and terminate in parallelend sections, means for securing said end sections together, and metallic lamentary means engaging the convergent portions only or" the laments, said means acting to increase the heat radiating capacity of said portions of the iilaments.

HOWARD D. DOOLITTLE.

REFERENCES CITED l The following references are of record in the file of this patent:

UNITED STATES PATENTS Crawford Apr. 23, 1946 

